A. Field of the Invention
The present invention relates to novel fillers for smoking article wrappers, and to processes for making them.
B. Description of the Prior Art
Sidestream smoke is the smoke given off by the burning end of a cigarette or a cigarette-like smoking article between puffs. Such smoke may be objectionable to some near the smoker who are not smoking or who do not smoke. Therefore, cigarettes that produce less sidestream smoke are highly desirable.
Several attempts have been made to reduce sidestream smoke through the use of various compounds as fillers for smoking article wrappers. For example, magnesium hydroxide and magnesium oxide have been reported to reduce sidestream smoke in cigarettes, as disclosed in U.S. Pat. Nos. 5,131,416, 4,941,485, 4,915,118, 4,881,557, 4,433,697, and 4,231,377. Some smokers find that cigarettes made with wrappers containing these compounds have an unacceptably poor taste.
Others have tried colloidal solutions of magnesium hydroxide, e.g. as disclosed by U.S. Pat. No. 4,450,847. Again, while magnesium hydroxide reduces the amount of sidestream smoke, its incorporation into smoking article wrappers often results in a cigarette with unacceptably poor taste.
Some have used physical mixtures of magnesium hydroxide or an unspecified "magnesium carbonate" composition with other compounds such as calcium carbonate in smoking article wrappers without solving the poor taste problem, as in U.S. Pat. No. 4,984,589.
Various grades of commercial basic magnesium carbonate, the standard industrial name for hydromagnesite, Mg.sub.5 (CO.sub.3).sub.4 (OH).sub.2 (4H.sub.2 O!, have been disclosed as the inorganic filler in cigarette papers to produce cigarettes having reduced sidestream smoke. One such example is U.S. Pat. No. 5,121,759. However, there is no teaching or suggestion in this disclosure regarding the particle size or morphology of the basic magnesium carbonates used. Generally, commercial basic magnesium carbonate (hydromagnesite) had been known for the manufacture of cigarette papers resulting in cigarettes with improved ash characteristics. See Papeterie, 1920, 42, 1021-1, 1065-9, and 1114-8; Chem. Abstr. 15, 1074.sup.4. Some have even tried flavoring agents to mask the poor taste.
However, none of these attempts to reduce the amount of sidestream smoke while maintaining positive subjective taste attributes have met with success.
The preparative chemistry and stability/reactivity of magnesium oxide, magnesium hydroxide, and the various carbonates of magnesium are very rich and very complicated in terms of stability fields and their characteristics of chemical transformations. As is the case for chemistry in general, a particular reaction can result in the formation of either the thermodynamically stable product(s), or kinetically controlled product(s), or various mixtures of products. In addition, solid products can be obtained in various particle sizes and morphologies. The chemistry described herein is complicated because one must consider all of the following: kinetic and thermodynamic stability; stability fields in terms of temperature, pressure, and concentration of materials; heterogeneous reaction conditions, which impact the formation and location of nucleation sites and crystallization characteristics; and the like.
Many references detail the production of synthetic basic magnesium carbonate (hydromagnesite Mg.sub.5 (CO.sub.3).sub.4 (OH).sub.2.4H.sub.2 O!), including U.S. Pat. Nos. 1,971,909, 1,361,324, 935,418; British Pat. Nos. 548,197 and 544,907; See also Z. Kst., 1910, 47, 118 and Z. Ch. Ind. Koll. 1909, 4, 189.) In these cases, aqueous solutions of magnesium bicarbonate Mg(HCO.sub.3).sub.2 ! were formed, typically incorporating a carbonation step, and then transformed by the action of base, e.g., magnesium hydroxide, to form basic magnesium carbonate. However, none of these attempts attempted, reported, or asserted the formation of compositions containing both hydromagnesite and magnesium hydroxide. In addition, none of these attempts specified examining various reaction conditions and varying molar ratios of carbon dioxide and other starting materials to form specific compositions containing both hydromagnesite and magnesium hydroxide. In addition, none of these attempts described any effort to modify morphology and obtain material sharing specific particle sizes and agglomerate sizes.
Nesquehonite (MgCO.sub.3.3H.sub.2 O) was formed by passing a 2-3% solution of magnesium bicarbonate through a series of tanks at about 38.degree. C. while magnesium oxide was added to the last tank, as disclosed in U.S. Pat. No. 2,549,408.
Hydromagnesite and magnesium hydroxide were obtained in the reaction of a soluble magnesium salt at relatively low temperatures by excess potassium carbonate or by potassium carbonate/potassium hydroxide. In this case, the initially formed precipitate is amorphous and later becomes crystalline, as described in H. Menzel and A. Brueckner, Z. Electrochem., 1930, 36, 63-87. If a magnesium-potassium mixed carbonate is used in the reaction, the products contain phases having both magnesium and potassium. (See L. Walter-Levy, Compt. rend. 1935, 200, 1940-1942.)
In another case, basic magnesium carbonate is treated with sodium hydroxide to yield pure magnesium hydroxide. (See Brit. Pat. No. 547,769.) The double decomposition of solutions of magnesium sulfate and potassium carbonate at the boiling point result in the formation of various double carbonates. (See L. Walter-Levy, Compt. rend. 1936, 203, 879-891.)
Mixtures containing various proportions of magnesium hydroxide, magnesite, and basic magnesium carbonate were prepared by the precipitation from a solution of magnesium sulfate with a mixture of solutions of sodium hydroxide and sodium carbonate. (See J. Berak, R. Guczalski, J. Wojcik and S. Zalwert, Przemysl Chem. 1960, 39, 298-300.)
A co-crystalline composition of magnesite and brucite, useful as a finer in a smoking article wrapper, and designed to reduce sidestream smoke without compromising subjective taste attributes, is described in commonly assigned U.S. Pat. No. 5,228,463.
Nonetheless, the search has continued for novel fillers for smoking article wrappers designed to reduce sidestream smoke without adversely affecting the consumer's subjective taste perception of the smoking article. The present invention was made as a result of that search.
C. Objects of the Invention
Accordingly, a primary object of this invention is to provide a smoking article and paper wrapper designed to reduce sidestream smoke without adversely affecting the consumer's subjective taste perception of the smoking article.
Another object of this invention is to develop compositions which can be used in a conventional papermaking process as filler material, either by itself or in a mixture with other filler materials such as calcium carbonate, along with natural plant fibers, the total mixture having rapid filtration capabilities.
Another object of the present invention is to provide processes for preparing compositions that are useful as fillers for fabrication of cigarette papers.
D. Summary of the Invention
In accordance with one aspect of the present invention, a process is provided for preparing an inorganic magnesium composition comprising the steps of:
(A) forming a first solution by one of the following: PA1 (B) heating the solution from step (A) to 45-55.degree. C. in the continued presence of carbon dioxide to form a second solution; and PA1 (C) adding an aqueous solution of an alkali base to the solution from step (B), and stirring the resulting mixture for an additional 4-8 hours at 80-90.degree. C. to form a precipitate. PA1 (a) mixing hydromagnesite with water to form a suspension; PA1 (b) reacting the suspension from step (a) with carbon dioxide to form a first solution; PA1 (c) reacting the solution from step (b) with magnesium acetate to form a second solution; and PA1 (d) adding an aqueous base solution to the solution from step (c) and heating the resultant mixture at or above 50(C to form a precipitate.
(i) mixing magnesium hydroxide, magnesium oxide, or a combination thereof, with water to form an aqueous suspension and reacting the suspension with carbon dioxide; PA2 (ii) reacting carbon dioxide with an aqueous suspension of at least one magnesium carbonate such as hydromagnesite, nesquehonite, lansfordite, dypingite, or georgiosite; PA2 (iii) reacting a water-soluble magnesium salt with an alkali metal bicarbonate in water to form an aqueous solution;
In accordance with another aspect of the present invention, steps (A) (i), (A) (ii) and (A) (iii) further comprise adding a water soluble magnesium salt such as magnesium acetate to the aqueous medium, preferably after the addition of the carbon dioxide.
In accordance with another aspect of the present invention, the filler for use in cigarette paper wrapper for a cigarette article comprising a magnesium carbonate hydroxide composition is produced by this process.
In accordance with another aspect of the present invention, a process is provided for preparing a magnesium carbonate hydroxide composition comprising the steps:
In accordance with another aspect of the present invention, a paper wrapper for a cigarette article is provided comprising plant fibers and a filler produced by the process of the present invention.
These and other objects, aspects and advantages of the present invention will become apparent from the following description.